Thyroiditis is an inflammation of the thyroid gland. There are many types of thyroiditis that cause various symptoms. Some types are chronic and progress slowly, whereas others are acute. Most types of thyroiditis are more common in women than men and tend to affect people over the age of 40.

An autoimmune disorder causes most cases of thyroiditis. Viral or bacterial infections cause some types of thyroiditis. Use of certain medications or treatments (e.g., radiation therapy) can also cause thyroiditis. The cause of some types of thyroiditis remains unknown.

Types of thyroiditis include:

• Hashimoto’s thyroiditis. This is the most common thyroid disorder in the United States, according to the Department of Health and Human Services, and the leading cause of hypothyroidism. This autoimmune condition often comes on slowly, unfolding over months or even years.
  
  
• Painless (silent) thyroiditis. Initially, this type of thyroiditis often causes a temporary increase in levels of thyroid hormones in the bloodstream (transient thyrotoxicosis) before hormone levels temporarily fall below normal (transient hypothyroidism). When thyrotoxicosis occurs, it can cause symptoms of hyperthyroidism.
  
  
• Postpartum thyroiditis. This condition is virtually identical to painless (silent) thyroiditis, except that it may occur only after a woman gives birth.
  
  
• Subacute thyroiditis. Also known as painful thyroiditis or DeQuervain’s disease, this type of thyroiditis is similar to painless (silent) thyroiditis, except that it causes throat pain and typically results from a viral infection.
  
  
• Infectious thyroiditis. Also known as acute suppurative thyroiditis, it is caused by a viral or bacterial illness, primarily the latter.
  
  
• Drug-related thyroiditis. Thyroiditis caused by the use of certain medications. It can lead to hypothyroidism and thyrotoxicosis.
  
  
• Radiation-induced thyroiditis. This type of thyroiditis may occur as a result of using radioactive iodine to treat hyperthyroidism or external beam radiation therapy to treat certain cancers. As with drug-induced thyroiditis, this type of thyroiditis can cause hypothyroidism and thyrotoxicosis.
  
  
• Riedel’s thyroiditis. This rare but potentially serious disorder involves the formation of fibrous tissue in the neck.

Symptoms of thyroiditis may differ, depending on the type of thyroiditis involved and the condition it has caused in a patient’s body. Slow, chronic damage to cells of the thyroid gland causes symptoms of hypothyroidism such as fatigue, constipation and unexplained weight gain. Acute damage may cause symptoms that mimic hyperthyroidism, such as a rapid heartbeat, insomnia and unexplained weight loss.

Most physicians diagnose thyroiditis by using thyroid function tests (e.g., blood testing) and radioactive iodine nuclear scans. Treatment options vary depending on the type of thyroiditis. Thyroid hormone replacement medications may be given to patients who experience hypothyroidism. Beta blockers, a type of antihypertensive, may be given to patients experiencing symptoms that mimic hyperthyroidism. There is no known method to prevent most cases of thyroiditis.